Positive, limited and negative responders: The variability in physical fitness adaptation to basic military training

Objectives: To investigate the heterogeneity of physical adaptation in Australian Army recruits completing a 12-week basic military training regimen. Design: A prospective research design. Methods: Volunteer recruits (n = 195) completed 12-weeks of basic military training. Recruit physical fitness was assessed at week 1, weeks 6–8 and week 12. Recruits in the upper (75th) and lower (25th) quartiles for each assessment were then analysed using a repeated measures two-way ANOVA. The relative magnitude of recruit adaptions were classified as positive response (Rpositive, ≥5%), limited response (Rlimited, >−5% to <5%) and negative response (Rnegative, ≤−5%); Chi-square analysis determined the proportional differences in the distribution of each quartile. Results: An interaction (p < 0.001) was observed in the lower and upper recruit quartiles for all assessments of physical fitness at each time point. After 12 weeks of military training the mean difference of the highest quartile was; 20-m multi-stage fitness test 7.4 mL·kg−1·min−1, (CI:5.8:9.1), 2-min push-ups 20.1 reps, (CI:16.2:23.9), 1RM box lift 5.6 kg, (CI:2.6:5.8) and load carriage 222.1 s, (CI:174.7:269.4) compared to the lowest recruit quartile. The highest quartile demonstrated no improvement in 1RM box lift (−4%, −1%) and push-ups (2%, 0%) performance at weeks 6–8 and week 12 respectively. In contrast, adaptations in the lowest quartile for 1RM box lift (16%, 21%) and push-ups (46%, 46%) over the same time periods were observed. Conclusions: A significant proportion of recruits may complete basic military training with a decline in physical performance. Higher relative-intensity cardiorespiratory and resistance exercise should be considered to facilitate physical adaptation in all recruits.